1. The Field of the Invention
This invention relates to distance measuring apparatus and more particularly to that class of device which displays the distance that is measured by the apparatus electronically at a location convenient to the user.
2. Description of the Prior Art
The prior art abounds with distance measuring instruments. U.S. Pat. No. 3,835,453 issued Sept. 17, 1974 to N. G. Polydoris teaches a measuring instrument for measuring linear distance on a surface by rolling a wheel on the surface along the linear distance to be measured. The wheel is mounted in a housing. The wheel is drivingly connected to a counter, which indicates the distance which the wheel has rolled. The counter is calibrated to indicate linear measurement in a selected system of measurement. A fastener is mounted in the housing. A collapsible handle is releasably connected to the fastener for manipulating the measuring instrument. The handle may be selectively removed from the instrument for convenient storage and handling. The Polydoris teachings suffer the deficiency of providing an indicating counter mounted adjacent the wheel and usable only in one selected system of linear measurement. Conversion factors must be employed in mathematically converting the system of measurement to any other desired measurement scheme. U.S. Pat. No. 3,251,132 issued May 17, 1966 to B. D. Hall discloses a wheel rotationally secured to the end of an elongated collapsible shaft having a mechanical counter secured thereto. The rotation of the wheel causes the counter to shift its digital-like display to preferred locations. A reset button is provided permitting the counter to be reset to a zero or starting position. Mechanical force, exerted on the wheel, must be of sufficient magnitude to operate the counter mechanism. Thus, the wheel perimeter, contacting the ground, must be pushed up against the ground with sufficient force so as to cause wear and tear thereon in order to effectively and reliably operate the counter, such being the case as well in the Polydoris teachings.
U.S. Pat. No. 1,401,913 issued Dec. 27, 1921 to D. G. Loraine describes a measuring device particularly suitable for measuring the length of a cable or cord when moving in contacting relationship with the perimeter of a wheel. A manually operated brake is disclosed such that the brake is utilized to prevent excessive rotation of the wheel, due to the inertia thereof, once having been started into motion by the motion of the line, cord or cable whose length is to be measured. A digital type mechanical counter is operated by the rotation of the wheel. The Loraine apparatus unfortunately possesses substantial inertia, due to its construction, thereby necessitating the use of the manually operated brake. This is in part due to the amount of friction required to operate the wheel, when contacting the line, cord or cable.
U.S. Pat. No. 1,718,052 issued Jan. 18, 1929 to W. C. Lineaweaver discloses a housing having a gear train mounted therein. One end of the gear train terminates in a wheel whose perimeter is partially permitted to be exposed, outwardly of the housing. The other end of the gear train is coupled to a clocklike hand which is rotationally mounted and secured outwardly of the housing. A circular scale is disposed beneath the hand and located on the exterior of the housing thereby indicating the number of revolutions taken by the wheel which extends outwardly from the housing. The Lineaweaver apparatus, though utilizing a small surface contacting wheel, is particular useful in measuring small distances, such as is normally encountered on maps, charts and the like. However, such small wheel is forced to operate a multiplicity of gears and an indicating hand, thus subjecting the wheel and other gear-like elements of the gear train to be easily worn and become useless.